Research Of The Beam-wave Interaction Of A 0.34THz Confocal Waveguide Gyro-TWT

With great application prospects,terahertz(THz)technology attracted great attention of many researchers.Gyrotron travel ing wave tube(gyro-TWT)is a very promising THz source since it is capable to provide THz radiation with high power,high efficiency and wide bandwidth.In order to provide enough power capacity,THz gyroTWT must operate at high order mode,which results in extreme mode competition.Confocal waveguide can operate at high order mode since the mode selectivity of transmission loss,has been demonstrated to be one of the interaction structure of THz gyro-TWT with great application prospect.This thesis focuses on the theory analyses of the beam-wave interaction of confocal waveguide gyro-TWT.The main content of this paper was chapter two to five,which is divided into four parts:1.The analyses of transmission characteristics of electromagnetic wave in confocal waveguide.Based on scalar diffraction theory,we obtained the field distribution equation of Gaussian beam.Then the distribution equation of vector field of mode was derived according to the boundary condition of confocal waveguide and the guided wave field theory.On these basis we analyzed the transmission loss of electromagnetic wave of different mode in confocal waveguide.The advantages of confocal waveguide to be the interaction structure of THz gyro-TWT was also introduced.Lastly,we designed an input coupler of confocal waveguide gyro-TWT,which verified the feasibility of mode conversion and transmission in confocal waveguide.2.The linear analysis of Beam-wave interaction: According to the kinetic theory,we introduced the Maxwel-Vlasov equation and the expansion of the field distribution equation according to the guiding center coordinate.Then the dispersion equation of kinetic theory for the beam-wave interaction of confocal waveguide gyro-TWT was obtained.On the basic of solving the dispersion equation we calculated the growth rate of electromagnetic wave as a function of frequency,and comparing it with the result of linearized single particle theory,which was widely applied in the linear analysis of confocal waveguide gyro-TWT.Lastly,the starting condition of absolute instability and backward wave oscillation was also analyzed based on the dispersion equation.3.The nonlinear theory of Beam-Wave interaction: In this part,we derived the expansion of electron motion equation in rectangular coordinates.And the self-consistent nonlinear derivation equations was also obtained.Then we introduced the numerical model of Beam-wave interaction and obtained the equations for calculation.4.With the combining of linear and nonlinear theory,numerical simulation and origin design for the 0.34-THz confocal waveguide gyro-TWT was introduced.In this part,we analyzed the influence of the operate parameters of electron beam,the electron distribution of electron beam and the transverse velocity spread to the beam-wave interaction,and the characteristic of harmonic operate was also analyzed.With the comparison of the results calculated from linear theory and nonlinear theory,we verified the validity of these two theories.On these basis we designed a 0.34-THz confocal waveguide gyro-TWT,analyzed the influence of voltage,operating magnetic field,operating frequency,velocity spread and input power to the Beam-Wave interaction.Lastly,we concluded the method and the main factors should be taken into consideration for the design of confocal waveguide gyro-TWT.